Vehicle lifespan may be increased by reducing stress loads upon structural components of the vehicle. The structural components often use stiffened panels and other structures bonded with ribs and stringers (stiffeners) to prevent the panel from buckling or otherwise failing when subjected to compressive loads. While stringers provide adequate reinforcement with respect to compressive loads, the stringer runouts, or areas at which the stringers terminate and interface with ribs, may experience premature failure due to local stress concentrations under certain conditions.
Traditionally, stringers utilize the runouts to terminate the stringers due to conflict with other structural components, such as the ribs, and the runouts inherently form local stress concentrations which reduce the useful life of the panel. Various techniques are used to reduce the local stress concentrations. But increasing skin and stringer thickness contributes to undesirable increases in cost and weight of the corresponding panel. Also, increased stiffness typically induces increased loads which may lead to premature failures.
Water may collect within the closed periphery of the interior of an assembled structural component. For example, in a vehicle such as an aircraft, water collects between joined upper and lower surfaces of a portion of a wing or a control surface such as flap, aileron, or elevator. A portion of a stringer enclosed within the structural component may be configured to permit water drainage across the stringer from one side to the other. For example, as shown in FIG. 1, a U-shaped cutout or opening may be machined into the web of the stringer that is big enough to create a water drain path and permit sufficient water drainage within the closed interior of the structural component.
Although the U-shaped cutout is needed for water drainage, the U-shaped cutout increases local stresses of the panel. Under flight conditions the current configuration of the U-shaped cutout creates a stress concentration that leads to premature failure of the closed structural component. Although a U-shaped cutout with a larger radius or curvature will reduce peak stress concentrations, the resulting reduced stresses will still result in earlier fatigue failure. Also, if a U-shaped cutout with a larger radius were machined into the stringer to reduce the stress concentrations enough to reduce premature failures, the radius of the enlarged U-shaped cutout would be larger than the height of the web of the stringer, which is impractical.
It is with respect to these and other considerations that the disclosure herein is presented.